Because this is a $$ deal in the end. By allowing only the book in question to be signed, it assures that the bookstore where the event is being held and the publishing company make money.That has been the drill on the most recent tours. Strictly enforced with military like precision. They even took purses away from the little old ladies in Maine to make sure no one carried a book in. I never understood why you couldn't purchase the book from the store holding the event to get your ticket but then get one book of your own choosing signed. But I have gave up arguing the logic of that approach where everyone leaves happy.